The Bubble-Mist Nets of the Spotted Dolphins
An animal that invents a tool always commands the respect of the ultimate gear species – us. One tool that dolphins use are bubbles. The Pacific spotted dolphins here in Costa Rica are so extremely proficient at blowing bubble nets that you would gasp with wonder at seeing the action. I did. Imagine you are approaching slowly by boat toward the birds that are the giveaway – a thick swarm of circling birds. Not just the booby and frigate birds that normally follow dolphins, but terns and shearwaters of multiple species not usually seen here with feeding dolphins. The birds dive continuously, some floating between dives instead of taking flight. They are staying above a dark shadow under the water.
Then you see a giant blob, an enormous stain like a slightly red shadow in the vast crystalline blue of the deep offshore Pacific. Sometimes ball-shaped, always amorphous, its two-story-house-sized form is always shifting, changing, flowing into new contours. It moves through the water, against the current. Then you see that it’s alive.
The cloud approaches you like a monstrous beast, engulfing you. Tiny fish, each just a few centimeters long, swarm all around you, darkening the light. Then the school shifts below, leaving you in the transparent blue again. As the huge shape-changing school of fish hovers a few meters below you, the dolphins fin out of the blue.
Pantropical spotted dolphins (Stenella attenuata), the most common of Costa Rica’s Pacific dolphins, are often found by the thousands. Bearing in mind these dolphins grow more spotted with age, you can tell you are watching a group of older dolphins, their flanks painted with dark and light spots. Whatever this group is up to, it’s not for kids.
With precise synchronization, the dolphins take deep breaths at the surface and dive directly below the cloud of fish. They move in formation, like a sports team using patterns and plays. Then begins the fine art of pantropical spotted dolphin bubble-mistnet hunting.
Down at the bottom of the school, one or two dolphins blow out a fine mist of tiny bubbles, making the water sparkle like champagne. The fizz explodes around the little fish, and more dolphins come in from the sides blowing mist nets. Groups of five or so dolphins then isolate small, extremely dense balls from the main mass. A slurp fest follows.
The wee bubbles, small as the head of a pin, cling to the half-finger-sized fish. Sticky bubbles cover the fish, rendering futile their puny efforts to escape the slurping dolphins.
Thousands of the little fish are swept up to the surface with the rising air, where the birds eat them in a frenzy.
Like kids with ice cream, the dolphins gulp the fish with dramatic body flair. Slashes, wiggles and shimmies erupt from the feeding group, and soon just a sprinkling of fish remains of the formerly dense balls separated from the main school. The dolphin’s shining bubbles, joining and expanding to a much larger size as they rise to less pressure, make it look as if a large group of scuba divers were below.
More dolphins move in for their turn, turning the water into a galaxy of bubbles, fish and tiny scales that glisten and shimmer like stars. The scales are scattered, shining everywhere, evidence of the massive consumption under way. Suitcase-sized tuna dart around, seemingly unable to produce a meal, snapping up a few stray fish slowed by leftover miniature bubble shrouds.
A huge sailfish, longer than you are, swims into the action, its heavy sword flashing threateningly toward you. The dolphins then display a behavior even more impressive than their use of the bubble-net tool.
They stop the bubbles and swim over, making a noisy ring around you. The great fish flashes right past, the big sword almost close enough to touch. The dolphins stay close a moment longer, no longer hunting or blowing any bubbles. You feel grateful for their assistance and wonder if the sailfish would have lanced you if the dolphins had not surrounded you.
Your heart is beating loud. Adrenaline floods your body.What else is out there in the thousand feet of purple below you? Below, the sailfish moves into the red cloud, slashing and trying to eat. The huge fish flashes its incredible electric-indigo and violet sail, scaring a few fish, but it’s not even close to a mouthful for the big beast. The sailfish darts around, frustrated with the tiny payback of food for the work, then finds and eats a few little baitfish left trapped in the clever bubblemist nets of the spotted dolphins.
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